This invention relates to an apparatus for testing a cross-coil instrument.
Cross-coil instruments have been used, for example, inelectrical speedometers for providing a vehicle velocity indication. Such cross-coil instruments include a pair of cross coils arranged to produce a magnetic field so as to move a pointer secured on a magnet when a voltage signal is applied thereto. The instrument also includes a velocity sensor which senses the existing vehicle velocity and generates a sensor signal having a frequency corresponding to the sensed vehicle velocity. The sensor signal is applied to a frequency-to-voltage converter where it is converted to a corresponding voltage signal which is applied to energize the cross coils.
The frequency-to-voltage converter is also connected through a manual switch to a test signal generator which generates a test signal having a predetermined frequency selected to move the pointer to a predetermined position when the instrument is operating in order. It is, therefore, possible to test the instrument from a view of the difference between the actual and the predetermined positions by operating the manual switch to connect the test signal generator to the frequency-to-voltage converter.
However, it is the current practice to place the manual switch on a circuit board on which the cross-coil gage is positioned. For this reason, an operator cannot operate the manual switch without troublesome operations removing the maintenance panel, the sound arrester plate and the meter cluster. It may be considered to place the manual switch at a position convenient for the operator. However, this is costly requiring additional parts such as harness switches, connectors, and the like.